Flexography is a direct rotary printing method which employs plates in relief made of photo-polymeric materials. The plates are flexible and soft, hence the name flexography. Such plates are inked and the print is obtained by means of direct deposition of the ink on the medium to be printed by virtue of a slight pressure exerted by a printing cylinder on which the plates are positioned.
Flexography is a high-speed printing process, capable of printing on many types of absorbing and non-absorbing materials. Some typical applications of flexographic printing are the production of paper and plastic bags, milk cartons, disposable cups and the like, but by virtue of the progress in printing quality, flexography is today also used for printing newspapers, for example, as well as packets and labels and for printing on plastic, films and acetate sheets, packing paper and on many other materials used for product packaging.
“Digital flexography” is a particular type of flexographic printing in which digital plates are used. In such plates, the photo-polymer is originally covered by a surface layer of material which prevents photo-exposure, such as for example a carbon or graphite layer. Such a layer of material is etched so as to create the negative image of the print subject. Such a step of etching is usually performed by means of a digital laser, controlled by a computer (hence the acronym CTP “Computer To Plate” used to indicate this step of the pre-printing process in the sector). The plate is then photo-exposed and the material not exposed to light is eliminated by washing with solvent or other liquid and then dried in an oven.
Systems which allow the production of digital plates according to the principle described above are known. These systems provide the use of various treatment stations, among which a photo-exposure station and a washing station, in which the material not exposed to light is eliminated from the plate after photo-exposure. Normally, these systems also comprise an oven, operatively downstream of the washing station, to dry the plate. Downstream of the oven, an exposure station may be further provided in which the plates are exposed to UV-A, to allow the polymerization of the parts of the polymer, generally at minimum size details of the image to be printed, which were not removed by the brushes while washing, and/or are exposed to UV-C, to eliminate the “stickiness” of the polymer.
On more recent versions, digital plate treatment systems extend substantially “in line”. Patent application EP 2839345 by the Applicant, for example, describes a system comprising a washing station in line with an exposure station and moving means which allow a continuous movement of the plate between the two treatment stations. Patent application WO 2016/030450 describes an in-line system conceptually similar to the one described in EP 2839345, in which a drying station of the flexographic plates is provided downstream of the washing station. Such a system comprises automatic moving means which pick the plates let out from the washing station and store them in specific drying boxes.
On some systems, the photo-exposure of the plate is performed in an autonomous treatment station, i.e. separated from the rest of the system comprising the washing station and the drying station. In this regard, patent application EP 3121653 describes an autonomous station for the photo-exposure of digital plates. In this case, at the end of the photo-exposure, the digital plate is picked and loaded into the washing station of the system. The latter may or may not be in line with the drying station.
On in-line systems, the plates are typically advanced through the treatment stations by using a pin bar to which the plate is coupled. Specifically, such a bar comprises a row of pins configured to be inserted into corresponding holes defined near a front edge of the plate, where the word “front” refers to the edge of the plate facing downstream with respect to a feeding direction of the plate. The pin bar is fed into the treatment station by means of a dragging system which is inside the station itself. More precisely, this system is configured to couple the opposite ends of the pin bar and to move it along said advancement direction. During such an advancement, the pin bar maintains an alignment direction transversal to the advancement direction by dragging the digital plate coupled thereto.
In systems of this type, the connection between plate and pin bar always requires a manual intervention. In particular, an operator firstly proceeds by piercing a plurality of holes through the plate in which the pins of the bar can be inserted. A punching device, in nearly all cases separate from the rest of the system, is used for this purpose. Once the holes are defined through the plate, the operator proceeds by manually connecting the plate to the pin bar (by inserting the pins into corresponding holes) and positioning the pin bar in a predetermined position near the inlet of the treatment station. In such a position, the pin bar can be coupled and dragged, together with the plate, by the dragging system inside the treatment station.
So, as a whole, the feeding of an in-line plant, and more in general of a treatment station, currently requires the manual intervention of an operator to load the plate, to connect the plate to the pin bar and finally to place the latter in the predetermined position for coupling it to the dragging system inside the first treatment station of the system. The need for a manual intervention is also found in systems in which the photo-exposure station is autonomous with respect to the in-line plant, in which the first treatment station is the washing station. In this case, the operator is required to perform a further intervention to physically transport the plate exiting from the exposure station to the punching device.
It is apparent that the manual loading of the plates is a clearly critical aspect in terms of costs. In addition to this, manual operations, despite their apparent simplicity, are intrinsically accompanied by a certain degree of risk. Furthermore, all the steps required by the loading process (piercing holes, connecting the plate to the pin bar and positioning the pin bar) are entrusted solely to the attention and the skill of the operators. This aspect is clearly critical in terms of reliability.
Given considerations above, it is the main task of the present invention to provide a feeding assembly for automatically loading a flexographic plate in a treatment station, which allows to overcome the drawbacks of the prior art. In the scope of this task, it is a first object of the present invention to provide a feeding assembly which allows the automatic connection, i.e. without the manual intervention of an operator, of a flexographic plate to a pin bar which can be dragged by a system inside the treatment station. It is another object of the present invention to provide a feeding assembly which allows a continuous loading, i.e. without interruptions and/or dead times. It is a not last object of the present invention to provide a feeding assembly which is reliable and easy to be manufactured at competitive costs.